Peripheral Control of the Assembly and Chirality of Anion-Based Octanuclear Cubes by Cation-π Networks.

Self-assembly of sophisticated polyhedral cages has drawn much attention because of their elaborate structures and potential applications. Herein, we report the anion-coordination-driven assembly of the first A8L12 (A = anion, L = ligand) octanuclear cubic structures from phosphate anion and p-xylylene-spaced bis-bis(urea) ligands via peripheral templating of countercations (TEA+ or TPA+). By attaching terminal aryl rings (phenyl or naphthyl) to the ligand through a flexible (methylene) linker, these aryls actively participate in the formation of plenty of "aromatic pockets" for guest cation binding. As a result, multiple peripheral guests (up to 22) of suitable size are bound on the faces and vertices of the cube, forming a network of cation-π interactions to stabilize the cube structure. More interestingly, when chiral ligands were used, either diastereomers of mixed Λ- and Δ-configurations (with TEA+ countercation) for the phosphate coordination centers or enantiopure cubes (with TPA+) were formed. Thus, the assembly and chirality of the cube can be modulated by remote terminal groups and peripheral templating tetraalkylammonium cations.

A Coordination-Derived Cerium-Based Amorphous-Crystalline Heterostructure with High Electrocatalytic Oxygen Evolution Activity.

The rational design of heterogeneous catalysts is crucial for achieving optimal physicochemical properties and high electrochemical activity. However, the development of new amorphous-crystalline heterostructures is significantly more challenging than that of the existing crystalline-crystalline heterostructures. To overcome these issues, a coordination-assisted strategy that can help fabricate an amorphous NiO/crystalline NiCeOx (a-NiO/c-NiCeOx ) heterostructure is reported herein. The coordination geometry of the organic ligands plays a pivotal role in permitting the formation of coordination polymers with high Ni contents. This consequently provides an opportunity for enabling the supersaturation of Ni in the NiCeOx structure during annealing, leading to the endogenous spillover of Ni from the depths of NiCeOx to its surface. The resulting heterostructure, featuring strongly coupled amorphous NiO and crystalline NiCeOx , exhibits harmonious interactions in addition to low overpotentials and high catalytic stability in the oxygen evolution reaction (OER). Theoretical calculations prove that the amorphous-crystalline interfaces facilitate charge transfer, which plays a critical role in regulating the local electron density of the Ni sites, thereby promoting the adsorption of oxygen-based intermediates on the Ni sites and lowering the dissociation-related energy barriers. Overall, this study underscores the potential of coordinating different metal ions at the molecular level to advance amorphous-crystalline heterostructure design.

AIE Ligand-Based Luminescent Ln-MOFs for Rapid and Selective Sensing of Tetracycline.

The design of highly stable and dual-emission lanthanide metal-organic frameworks (Ln-MOFs) is promising for practical chemical sensor applications. Rational design and synthesis of photoresponsive organic ligands provide a feasible approach to achieving highly fluorescent dual-emission Ln-MOFs. In this study, a tetraphenylpyrazine-based AIE ligand, H4L, was synthesized and combined with lanthanide ions (including Sm3+, Eu3+, Gd3+, and Tb3+) to fabricate a series of Ln-MOFs named Ln-L. The single-crystal analysis revealed that all Ln-L belonged to the tetragonal space group P4212 and featured a 2-fold interpenetrated 3D structure. Leveraging rational design, Eu-L exhibited a sensitive response to tetracycline, making it a promising fluorescence sensor for tetracycline detection. The experiments demonstrated that Eu-L could rapidly and quantitatively detect tetracycline and its analogs within 30 s. The lowest detection limits for tetracycline, oxytetracycline, and chlortetracycline were 0.43, 0.92, and 0.81 µM, respectively. Additionally, the probe displayed excellent reusability and exceptional selectivity. A plausible sensing mechanism was proposed, supported by both experimental and theoretical analyses. Furthermore, the study discovered that on-site and real-time determination of TCs in aqueous solutions could be achieved by using luminescence test papers and composite films derived from Eu-L.

Constructing Ultrastable Metallo-Cages via In Situ Deprotonation/Oxidation of Dynamic Supramolecular Assemblies.

Coordination-driven self-assembly enables the spontaneous construction of metallo-supramolecules with high precision, facilitated by dynamic and reversible metal-ligand interactions. The dynamic nature of coordination, however, results in structural lability in many metallo-supramolecular assembly systems. Consequently, it remains a formidable challenge to achieve self-assembly reversibility and structural stability simultaneously in metallo-supramolecular systems. To tackle this issue, herein, we incorporate an acid-/base-responsive tridentate ligand into multitopic building blocks to precisely construct a series of metallo-supramolecular cages through coordination-driven self-assembly. These dynamic cagelike assemblies can be transformed to their static states through mild in situ deprotonation/oxidation, leading to ultrastable skeletons that can withstand high temperatures, metal ion chelators, and strong acid/base conditions. This in situ transformation provides a reliable and powerful approach to manipulate the kinetic features and stability of metallo-supramolecules and allows for modulation of encapsulation and release behaviors of metallo-cages when utilizing nanoscale quantum dots (QDs) as guest molecules.

A Diverse Array of Large Capsules Transform in Response to Stimuli.

The allosteric regulation of biomolecules, such as enzymes, enables them to adapt and alter their conformation to fit specific substrates, expressing different functionalities in response to stimuli. Different stimuli can also trigger synthetic coordination cages to change their shape, size, and nuclearity by reconfiguring the dynamic metal-ligand bonds that hold them together. Here we demonstrate an abiological system consisting of different organic subcomponents and ZnII metal ions, which can respond to simple stimuli in complex ways. A ZnII20L12 dodecahedron transforms to give a larger ZnII30L12 icosidodecahedron through subcomponent exchange, as an aldehyde that forms bidentate ligands is displaced in favor of one that forms tridentate ligands together with a penta-amine subcomponent. In the presence of a chiral template guest, the same system that produced the icosidodecahedron instead gives a ZnII15L6 truncated rhombohedral architecture through enantioselective self-assembly. Under specific crystallization conditions, a guest induces a further reconfiguration of either the ZnII30L12 or ZnII15L6 cages to yield an unprecedented ZnII20L8 pseudo-truncated octahedral structure. The transformation network of these cages shows how large synthetic hosts can undergo structural adaptation through the application of chemical stimuli, opening pathways to broader applications.

Metallo-Supramolecular Hexagonal Wreath with Four Switchable States Based on a pH-Responsive Tridentate Ligand.

In biological systems, many biomacromolecules (e.g., heme proteins) are capable of switching their states reversibly in response to external stimuli, endowing these natural architectures with a high level of diversity and functionality. Although tremendous efforts have been made to advance the complexity of artificial supramolecules, it remains a challenge to construct metallo-supramolecular systems that can carry out reversible interconversion among multiple states. Here, a pH-responsive tridentate ligand, 2,6-di(1H-imidazole-2-yl)pyridine (H2DAP), is incorporated into the multitopic building block for precise construction of giant metallo-supramolecular hexagonal wreaths with three metal ions, i.e., Fe(II), Co(II), and Ni(II), through coordination-driven self-assembly. In particular, a Co-linked wreath enables in situ reversible interconversion among four states in response to pH and oxidant/reductant with highly efficient conversion without losing structural integrity. During the state interconversion cycles, the physical properties of the assembled constructs are finely tuned, including the charge states of the backbone, valency of metal ions, and paramagnetic/diamagnetic features of complexes. Such discrete wreath structures with a charge-switchable backbone further facilitate layer-by-layer assembly of metallo-supramolecules on the substrate.

Self-assembly-induced luminescence of Eu3+-complexes and application in bioimaging.

Design and engineering of highly efficient emitting materials with assembly-induced luminescence, such as room-temperature phosphorescence (RTP) and aggregation-induced emission (AIE), have stimulated extensive efforts. Here, we propose a new strategy to obtain size-controlled Eu3+-complex nanoparticles (Eu-NPs) with self-assembly-induced luminescence (SAIL) characteristics without encapsulation or hybridization. Compared with previous RTP or AIE materials, the SAIL phenomena of increased luminescence intensity and lifetime in aqueous solution for the proposed Eu-NPs are due to the combined effect of self-assembly in confining the molecular motion and shielding the water quenching. As proof of concept, we also show that this system can be further applied in bioimaging, temperature measurement and HClO sensing. The SAIL activity of the rare-earth (RE) system proposed here offers a further step forward on the roadmap for the development of RE light conversion systems and their integration in bioimaging and therapy applications.

Eu3+/Tb3+ supramolecular assembly hybrids for ultrasensitive and ratiometric detection of anthrax spore biomarker in water solution and actual spore samples.

Rare earth (RE) complexes have found a variety of applications in materials science and biomedicine because of their unique luminescence properties. However, the poor stability and solubility in water of multicomponent RE assemblies significantly limit their practical applications. We rationally designed and developed a novel Eu3+/Tb3+ supramolecular assembly hybrids (Eu/Tb-SAH) by supramolecular host-guest recognition and coordination recognition with the excellent characteristics of water dispersion stability, biocompatibility and luminous properties. As anthrax spore biomarker, 2,6-pyridinedicarboxylic acid (DPA) can coordinate with Tb3+ and sensitize Tb3+, resulting in a proportional change of fluorescence intensity and lifetime on the ms timescales, thereby realizing rapid and sensitive detection of DPA in water media or actual spores. To confirm our prediction, accurate and selective detection of DPA was achieved with Eu/Tb-SAH as a nanoprobe through steady-state ratiometric fluorescence and time-resolved technology, of which the limit of detection (LOD) are 27.3 nM and 1.06 nM, respectively. This was obviously lower than the amount of anthrax spores infecting the human body (60 µM). Besides, the filter paper was used to carry out visual detection of DPA and read the corresponding data through smart phones. This work paves a new way to fabricate luminescent RE nanomaterials and provides new ideas for the design of ratiometic lifetime imaging biosensors in the meantime.

A TAT peptide-based ratiometric two-photon fluorescent probe for detecting biothiols and sequentially distinguishing GSH in mitochondria.

Although biothiols, including cysteine (Cys), glutathione (GSH), and homocysteine (Hcy) can be used to diagnose many diseases and research physiological metabolism in many physiological processes, in situ real-time detection and differentiation of biothiols is still challenging because their similar chemical properties and molecular structures. Herein, we utilized the native chemical ligation (NCL) reaction mechanism to develop a Förster resonance energy transfer (FRET) strategy for designing a cell penetration peptide TAT-modified ratiometric two-photon biothiols probe (TAT-probe). The TAT-probe can not only rapidly enter into mitochondria assisted by TAT peptide, but also simultaneously detect biothiols and sequentially distinguish GSH. When the TAT-probe was excited with 404/820 nm wavelength light, it showed a change in the ratio of fluorescence after adding biothiols, including a quenched red fluorescence intensity (λem = 585 nm) and an enhanced signal in green fluorescence intensity (λem = 520 nm). Excitingly, the TAT-probe excited at 545 nm could display a red fluorescence (λem = 585 nm) towards GSH and a quenched signal towards Hcy or Cys. This specific fluorescence response indicated the TAT-probe could effectively detect biothiols and differentiate GSH from Cys/Hcy in mitochondria. This work pioneered a new approach to design and synthesize biothiol-probes based on peptides and NCL reaction mechanism.

Smart MMP2-Responsive Nanoprobe for Activatable Fluorescence Imaging-Guided Local Triple-Combination Therapies with Single Light.

Elaborately designed stimuli-responsive smart systems simultaneously enabling activatable imaging and selective treatment are highly desirable for precise diagnosis and therapy of cancer. Herein, such a smart theranostic nanoprobe composed of hollow gold nanospheres (HAuNs), photosensitizer (PS), matrix metalloproteinase 2 (MMP2) substrate peptide, and model drug doxorubicin (DOX) was designed. In the design, HAuNs served as the acceptor of Förster resonance energy transfer (FRET), photothermal therapy (PTT) reagent, and nanocarrier. The fluorescence and 1O2 generation of PS were inhibited by HAuNs through FRET effect, avoiding phototoxicity to normal tissues during circulation. Meanwhile, owing to the MMP2-triggered peptide cleavage, the PS could be efficiently activated in a tumor for selective fluorescence imaging and photodynamic therapy (PDT). The recovered fluorescence could be applied for detecting MMP2, locating tumor in vivo, and further guiding the local triple-combination therapies including PDT, PTT, and chemotherapy. The synergistic treatments of activated PDT, PTT, and controlled DOX release were achieved with single light, which provided the best therapeutic effects with enhanced stability and remarkably reduced nonspecific toxicity of PS and anticancer drug. This study helps to design novel stimuli-responsive systems for precise molecular sensing and site-specific cancer treatment.

Eu2+/Eu3+-Based Smart Duplicate Responsive Stimuli and Time-gated Nanohybrid for Optical Recording and Encryption.

With the rapid development of information science, it is urgent that memory devices possessing high security, density, and desirable storage ability should be developed. In this work, a smart duplicate response of stimuli has been developed and a time-gate nanohybrid based on variable valence Eu2+/Eu3+ coencapsulated has been fabricated and acts as active material in the multilevel and multidimensional memory devices. The luminescence lifetime of Eu3+ in this nanohybrid gave a stimuli response due to which the energy level of the coordinated ligand could be modulated. Furthermore, by a simple sintering procedure, Eu3+ was partially in situ reduced to Eu2+ with a short lifetime in the system. And the in situ reduction ensured both Eu3+ and Eu2+ ions' uniform distribution in the nanohybrid and simultaneous response upon light excitation of variable valence Eu ions. Interestingly, Eu3+ revealed a prolonged lifetime because of the presence of an energy-transfer effect of Eu2+ → Eu3+. Such a nanohybrid had abundant luminescent properties, including the short lifetime of Eu2+, the energy transfer from the Eu2+ to Eu3+ ions, and the stimuli response of the Eu3+ lifetimes when exposed to acidic or basic vapor, thus giving birth to interesting recording and encryption performance in spatial-temporal dimensions. We believe that this research will point out a new direction for the future development of multilevel and multidimensional optical recording and encryption materials.

A novel peptide-based fluorescence chemosensor for selective imaging of hydrogen sulfide both in living cells and zebrafish.

Hydrogen sulfide (H2S) plays an important role as a signaling compound (gasotransmitter) in living systems. However, the development of an efficient imaging chemosensor of H2S in live animals is a challenging field for chemists. Herein, a novel peptide-based fluorescence chemosensor L-Cu was designed and synthesized on the basis of the copper chelating with the peptide ligand (FITC-Ahx-Ser-Pro-Gly-His-NH2, L), and its H2S sensing ability has been evaluated both in living cells and zebrafish. The peptide backbone and Cu2+-removal sensing mechanism are used to deliver rapid response time, high sensitivity, and good biocompatibility. After a fast fluorescence quench by Cu2+ coordinated with L, the fluorescence of L is recovered by adding S2- to form insoluble copper sulfide in aqueous solution with a detection limit for hydrogen sulfide measured to be 31nM. Furthermore, the fluorescence chemosensor L-Cu showed excellent cell permeation and low biotoxicity to realize the intracellular biosensing, L-Cu has also been applied to image hydrogen sulfide in live zebrafish larvae. We expect that this peptide-based fluorescence chemosensor L-Cu can be used to study H2S-related chemical biology in physiological and pathological events.

Fluorescence "on-off-on" peptide-based chemosensor for the selective detection of Cu2+ and S2- and its application in living cell bioimaging.

Copper ions are known to be very important for homeostasis, which is critical for the metabolism and development of living organisms. In addition, sulfide ions, as an important endogenously produced gasotransmitter, have been proved to be implicated in a variety of physiological functions such as anti-apoptosis, vasodilation, antioxidation, and anti-inflammation. Herein, we report the development of a novel fluorescence chemosensor (L) based on a tetra-peptide conjugated with dansyl groups as a promising analytical tool for detecting Cu2+ and S2- in 100% aqueous solutions, which exhibits excellent cell biotoxicity and intracellular biosensing ability. The chemosensor L displays an "on-off-on" response type fluorescence change upon the addition of Cu2+ and S2- to aqueous media and living cells. Moreover, L displays high selectivity and sensitivity with the detection limits for Cu2+ and S2- measured to be 88 nM and 75 nM, respectively. This study raises the new possibility of a highly selective and sensitive peptide-based fluorescence chemosensor for multifunctional detection, including cation and anions, using a successive fluorescence response strategy in environmental and biological systems.

Relationship between reaction rate constants of organic pollutants and their molecular descriptors during Fenton oxidation and in situ formed ferric-oxyhydroxides.

Fenton oxidation is a promising water treatment method to degrade organic pollutants. In this study, 30 different organic compounds were selected and their reaction rate constants (k) were determined for the Fenton oxidation process. Gaussian09 and Material Studio software sets were used to carry out calculations and obtain values of 10 different molecular descriptors for each studied compound. Ferric-oxyhydroxide coagulation experiments were conducted to determine the coagulation percentage. Based upon the adsorption capacity, all of the investigated organic compounds were divided into two groups (Group A and Group B). The percentage adsorption of organic compounds in Group A was less than 15% (wt./wt.) and that in the Group B was higher than 15% (wt./wt.). For Group A, removal of the compounds by oxidation was the dominant process while for Group B, removal by both oxidation and coagulation (as a synergistic process) took place. Results showed that the relationship between the rate constants (k values) and the molecular descriptors of Group A was more pronounced than for Group B compounds. For the oxidation-dominated process, EHOMO and Fukui indices (f(0)x, f(-)x, f(+)x) were the most significant factors. The influence of bond order was more significant for the synergistic process of oxidation and coagulation than for the oxidation-dominated process. The influences of all other molecular descriptors on the synergistic process were weaker than on the oxidation-dominated process.

QSAR models for removal rates of organic pollutants adsorbed by in situ formed manganese dioxide under acid condition.

Manganese dioxide formed in oxidation process by potassium permanganate exhibits promising adsorptive capacity which can be utilized to remove organic pollutants in wastewater. However, the structure variances of organic molecules lead to wide difference of adsorption efficiency. Therefore, it is of great significance to find a general relationship between removal rate of organic compounds and their quantum parameters. This study focused on building up quantitative structure activity relationship (QSAR) models based on experimental removal rate (r(exp)) of 25 organic compounds and 17 quantum parameters of each organic compounds computed by Gaussian 09 and Material Studio 6.1. The recommended model is rpre = -0.502-7.742 f(+)x + 0.107 E HOMO + 0.959 q(H(+)) + 1.388 BOx. Both internal and external validations of the recommended model are satisfied, suggesting optimum stability and predictive ability. The definition of applicability domain and the Y-randomization test indicate all the prediction is reliable and no possibility of chance correlation. The recommended model contains four variables, which are closely related to adsorption mechanism. f(+)x reveals the degree of affinity for nucleophilic attack. E HOMO represents the difficulty of electron loss. q(H(+)) reflect the distribution of partial charge between carbon and hydrogen atom. BO x shows the stability of a molecule.

A novel fluorescent chemosensor based on tetra-peptides for detecting zinc ions in aqueous solutions and live cells.

A fluorescent chemosensor is a powerful analytical tool for the visualization and quantitation of analytes in living cells, tissue slices, and whole bodies. Peptides with a reporter ionophore are very valuable as fluorescent chemosensors, because of their higher biological compatibility and solubility compared to organic dyes, and they are more stable than proteins in aqueous solutions. Herein, we report a novel peptide fluorescent chemosensor (HL) based on tetra-peptides conjugated with dansyl groups, which was synthesized by solid phase peptide synthesis. This chemosensor selectively and sensitively detects Zn2+ based on the photo-induced electron transfer (PET) effect by turn-on response in 100% aqueous solutions. As designed, HL can penetrate live HeLa cells and image intracellular Zn2+ by turn-on response. Moreover, HL exhibits low biotoxicity with a limit of detection (LOD) of about 32 nM for Zn2+, implying that HL acts as a highly useful peptide fluorescent chemosensor for biological systems.